Re-entrant relaxor ferroelectric behaviour in Nb-doped BiFeO₃–BaTiO₃ ceramics

Abstract

Re-entrant relaxor ferroelectric behaviour is identified in BiFeO3–BaTiO3 ceramics, yielding anomalous thermal variations in structural distortion and functional properties.

Temperature-Dependent Ferroelectric Properties and Aging Behavior of Freeze-Cast Bismuth Ferrite–Barium Titanate Ceramics

“…The value of the α ε coefficient for the porous sample increased sharply to α ε = 0.862 mm/V, 2.5 times larger than that of the dense ceramic ( α ε = 0.328 mm/V) as temperature increased to 100 °C, which is close to the Rayleigh coefficient reported for the BaTiO 3 modified BiFeO 3 –PbTiO 3 piezoceramic system (1.1 mm/V) . Increases in the rhombohedral distortion with temperature may play a key role in the large increase in α ε coefficient at 100 °C by making it possible to convert the ferroelectric domain structure to a relaxor state . Another possible contributor is the 30% drop in the coercive field for the porous material at this temperature compared to a 23% drop for the dense sample.…”

“…For the entire frequency range, all of the porous specimens had lower relative permittivity than the dense BFBT30 ceramics, with permittivity decreasing as a function of porosity in all cases. Dielectric loss was observed to be lowest around 1 kHz and increased for frequencies above 3 kHz, which may be due to dipolar losses associated with re-entrant relaxor ferroelectric behavior observed recently in BF-BT . At frequencies below 500 Hz the loss tangent is inversely proportional to frequency and is attributed to the effects of DC conductivity, which also leads to an increase in the measured permittivity in this region.…”

“…Dielectric loss was observed to be lowest around 1 kHz and increased for frequencies above 3 kHz, which may be due to dipolar losses associated with re-entrant relaxor ferroelectric behavior observed recently in BF-BT. 48 At frequencies below 500 Hz the loss tangent is inversely proportional to frequency and is attributed to the effects of DC conductivity, which also leads to an increase in the measured permittivity in this region. The dielectric loss was not significantly affected by the presence of a porosity.…”

“…The absolute value of the coercive field decreased with increasing temperature for all samples, leading to enhanced electric field induced ferroelectric switching with a slim hysteresis loop. A recent study on a similar composition showed that the rise in polarization with temperature may be attributable to an abnormal increase in rhombohedral distortion, which is associated with the re-entrant relaxor ferroelectric transition when heated from room temperature to ∼200 °C …”

“…A recent study on a similar composition showed that the rise in polarization with temperature may be attributable to an abnormal increase in rhombohedral distortion, which is associated with the re-entrant relaxor ferroelectric transition when heated from room temperature to ∼200 °C. 48 The saturation (P s ) and remnant polarization (P r ) values of the porous ceramics were lower than those of dense materials at both room (RT) and elevated temperatures due to the lower volume of active ferroelectric material and the high volume of low permittivity pores. At RT and 40 kV/cm field strength, the P s and electrostrain of the dense specimen was 16 μC/cm 2 and 0.05% respectively (Figure 8a).…”